One thing I can attest from spending as much time watching the Leveson Inquiry as at sundry inquiries into the Iraq war: never has such a vast amount of legal time been poured into dissecting the workings of the British press. With more payouts due, many will think this comeuppance for phone hacking and other crimes, some serious and some comically venal. Did Lord Justice Leveson, for instance, really need to re-call the Sun's editor yesterday to ask if ladies in states of undress on Page 3 are a national abomination? It would be a very constrained press indeed which forbids a publisher from bringing us entirely legal images of Tracy from Wapping getting her kit off.

As tempers fray, the tone becomes more supercilious and ever more extraneous evidence is dragged before the investigation. Aside from the proper task of looking into which regulatory framework would fend off future law-breaking better than the wan Press Complaints Commission, the danger is mission creep, and it is not so much creeping as galloping.

Lord Leveson is a pithy inquisitor of the type the Establishment has long since decided should sit in final judgment on everything from missing WMD to how Heat magazine gets its celebrity scoops. He has a keen ear for nonsense jargon: when a counsel yesterday cited a "window of opportunity for a video link", Lord Leveson repeated the phrase with the distaste Lady Bracknell reserved for "A handbag?" He expects candour and nags at evasive witnesses until he gets it.

But the worry, observing both his interjections and lines of his questioning, is that he exhibits a lawyer's deformation professionelle when it comes to a lively interest in how to constrain the press, whether through fines or new regulatory bodies, without an accompanying curiosity about its freedoms or indeed its spirit. Thus we ended up last night with Robert Jay QC pursuing in all seriousness whether the tabloids can presume consent in running features about Pippa Middleton's bottom.

There is enough irrelevant inquiry here to keep Dickens's Jarndyce and Jarndyce in work for decades, along with exploration of which slang should be allowed in headlines - I suggest a new regulator, Ofpun - and whether articles about underwear are "eroticising". Quite what this has to do with an event arising from phone hacking, I am unclear.

The freedom to create and commercially sustain a variety of newspapers, catering to different tastes and using different vernacular, is a hard-fought one and worth defending, as it tends to disappear when people do not understand that the press is a fragile and shifting entity whose survival is only guaranteed by being responsive and fighting hard for shrinking markets.

Both this newspaper's proprietor and the Guardian's editor have said that Britain's papers are "under-regulated and over-legislated", reflecting that the PCC must be more obviously effective and that constrictive libel laws, impeding investigative journalism and serving rich people's whims, need to change. No one could sit through Lord Leveson's inquiry and not conclude that something big is shifting in the way Fleet Street's rough old trade is governed. But beware a retributive mood and legal creep which sets out to cure a licentious press, only to curtail a lively and useful one.